The present invention relates to a subscriber's circuit controlling apparatus for a time division switching system which serves analog subscribers, and in particular to a subscriber's circuit controlling apparatus and a switching system for controlling subscriber's circuit devices based upon a random control system in response to control information from a host apparatus.
A conventional subscriber's circuit controlling apparatus for a time division switching system has been known as is described in "A Study Configuration of Small Capacity Speech Path System" the Institute of Electronics, Information and Communication Engineers (IEICE) autumn 1989. In the conventional, the subscriber's circuit controlling apparatus receives subscriber's circuit control information from a central control system in a host switching system and transfers an order to corresponding subscriber's circuit for controlling the same. Main functions of a subscriber's circuit controlling apparatus 1 are shown in Table 1.
TABLE 1 ______________________________________ FUNCTION NAMES SUMMERY OF FUNCTIONS ______________________________________ LOOP STATE TO NOTIFY A CENTRAL MONITORING PROCESSING DEVICE OF DETECTION OF LOOP IN ALL SUBSCRIBER'S CIRCUITS MAINTENANCE TO MONITOR OPERATING STATE MONITORING OF ALL SUBSCRIBER'S CIRCUITS AND TO NOTIFY AN ALARM PAD/FILTER TO CONTROL PROSETTING OF PROSETTING VARIOUS FILTERS/PADS ON CONTROL AND LOG SUBSCRIBER'S LINES FIRST RINGING TO NOTIFY VARIOUS RINGING CONTROL PATTERNS. TO CONTROL START FROM RINGING ON STATE. TIME SLOT TO CONTROL CONNECTION/ CONTROL DISCONNECTION BETWEEN A NETWORK AND EACH SUBSCRIBER'S CIRCUIT RING TRIP TO IMMEDIATELY STOP RINGING AFTER RESPONDING TO CALLING POW-ON TO CONTROL SWITCHING BETWEEN OPERATIVE AND INOPERATIVE STATES OF SUBSCRIBER'S CIRCUIT DUAL SYSTEM TO SWITCH TO STAND-BY SYSTEM SWITCHING VALUE CURRENTLY OPERATIVE SYSTEM IS FAULTY IN DUPLEX REDUNDANT STRUCTURE ______________________________________
As shown in Table 1, the subscriber's circuit controlling apparatus 1 performs detection of the loop of a subscriber's circuit and monitoring of maintenance information and executes the task of the control information corresponding to a result of the detection and monitoring. The subscriber's circuit controlling apparatus 1 transfers the control information to the subscriber's circuits in accordance with a control order representative of an instruction and the address of a subscriber's circuit from the central processing device 21. Types of control order are shown in Table 1 and codes corresponding to respective types are preliminarily allocated to the control orders.
Systems for controlling the communication between the subscriber's controlling apparatus and the subscriber's circuit devices include a cyclic control system in which the control information is time-division-multiplexed on a control bus for cyclically transferring control signals to the subscriber's circuit controlling apparatus and a random control system in which control information from a host switching system is analyzed and only necessary control information is edited so that a control signal is transferred to the subscriber's circuit device as shown in FIG. 9. Functions in two systems are compared with each other in Table 2.
TABLE 2 __________________________________________________________________________ SYSTEM ITEM CYCLID CONTROL SYSTEM RANDOM CONTROL SYSTEM __________________________________________________________________________ PROCESSING REDUNDANCY IS HIGH SINCE X ORDER IS TRANSFERRED TO .largecircle. CAPACITY THE CONTROL INFORMATION IS SUBSCRIBER'S CIRCUIT IN TRANSFERRED CYCLICALLY TRANSFERRED RESPONSE TO HOST APPARATUS EFFICIENCY WHETHER OR NOT HOST CONTROL CONTROL INFORMATION. INFORMATION IS ISSUED. FUNCTION FUNCTION CONCENTRATION TO .largecircle. SAME AS LEFT COLUMN .largecircle. CONCENTRATION CONTROLLING APPARATUS SIDE IS POSSIBLE. IT SUFFICES FOR SUBSCRIBER'S CIRCUIT TO HAVE CAPABILITY OF SIMPLY RECOGNIZING AND EXECUTING RECEIVED ORDER. IMMUNITY ORDERS AFE CYCLICALLY .largecircle. IF THERE IS NO DEVICE .DELTA. TO TRANSFERRED. MALFUNCTION ON PREVENT INTERMITTENT INTERMITTENT INTERMITTENT FAULT CAN BE FAULT IN TRANSFER FAULT RECOVERED IN NEXT CYCLE. PROCEDURE, MALFUNCTION DUE TO THE INTERMITTENT FAULT CAN NOT BE PREVENTED. MALFUNCTION PREVENTION PROCEDURE IS NECESSARY. ADAPTABILITY ENHANCEMENT IN WRITE SPEED .largecircle. MEANS FOR PREVENTING .DELTA. ON ORDER OF STATE STORING MEMORY INFORMATION MISSING WHICH CONGESTION MAKES ADAPTATION EASIER. OTHERWISE OCCURS ON CONGESTION OF HOST ORDERS OR WHEN THE ORDER TRANSFER AND PROCESSING CAPACITY IS LOWERED.(ORDER QUEUE BUFFER) RELIABILITY SINCE DUAL REDUNDANT .largecircle. DEVICE IS NECESSARY .DELTA. STRUCTURE IS ADOPTED. WHICH CAN CONTROL SYSTEM SYSTEM SWITCHING CONTROL IS SWITCHING WITHOUT EASY. DISCARDING OF ORDERS ALTHOUGH DUAL REDUNDANT STRUCTURE IS ADOPTED. FLEXIBILITY SINCE FIXED ALLOCATION X EXPANSION IS EASY BY ONLY .largecircle. EXPANDABILITY TRANSFER IS PERFORMED, INCREASING THE NUMBER OF EXPANSION IS DIFFICULT. ORDER KINDS. HARDWARE THE SYSTEM CAN BE .DELTA. THE SYSTEM CAN BE .DELTA. SCALE IMPLEMENTED BY LOGICAL IMPLEMENTED BY LOGICAL HARDWARE. CONTROL OF STATE HARDWARE. HARDWARE SUCH AS STORAGE MEMORY IS SLIGHTLY QUEUE BUFFER IS NEEDED. COMPLICATED. __________________________________________________________________________
As shown in Table 2, the cyclic control system has heretofore been adopted to cope with malfunctions (intermittent faults) which occurs due to noise which is generated on a common control bus for the linkage between the subscriber's circuit controlling apparatus and the subscriber's circuits when a hot-line job of a subscriber's circuit device is inserted or removed. In other words, even if malfunction temporarily occurs due to noise, the malfunction will not continue since a correct control signal is transmitted in the next cycle. In contrast to this, a malfunction may occur in the random control system.
The cyclic control system needs to cyclically transfer each control order to each subscriber's circuit device even when there is no access from the host switching system. Therefore, the cyclic control system has a high redundancy and a limited amount of control information. Accordingly, if the amount of control information is increased in association with an advancement in function of subscriber's circuit controlling apparatus and an increase in the number of subscriber's circuit devices, a higher information transfer rate or expandability of the control bus is needed for the cyclic control system to achieve a control order in which initial presetting control or diagnosis test control occurs at a low frequency and the amount of information is high. As a result of this, the cyclic control system becomes more complicated.
Although the random control system can cope with the increase in the amount of control information, it has problems in the above mentioned malfunction due to noise generated on insertion or removal of a plug of the subscriber's circuit board and missing of the control information occurring when the transfer and processing capacity is limited due to the increase in the amount of control information.
A problem arises that the control information is discarded on switching of systems if the subscriber's circuit controlling apparatus adopts the duplex system of redundant structure.